Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 51
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Langmuir ; 2020 Mar 17.
Artigo em Inglês | MEDLINE | ID: mdl-32134667

RESUMO

This study investigated Janus particles (JPs) composed of an azo polymer and a pyrene-containing polymer, focusing on preparation, formation mechanism, photoinduced deformation behavior, and fluorescent properties as well as tunable colors of the dispersions. A methacrylate-based copolymer containing pyrenyl groups (P(MMA-co-PyMA)) and two azo polymers, i.e., a methacrylate-based polymer (PCNAZO) and an epoxy-based polymer (CH-TZ-NT) both bearing push-pull-type azo chromophores, were synthesized for this purpose. Two types of Janus particles, P(MMA-co-PyMA)/PCNAZO JPs and P(MMA-co-PyMA)/CH-TZ-NT JPs, were fabricated through microphase separation of the components in the droplets dispersed in aqueous media, induced by the evaporation of the organic solvent. The process of JP formation was thoroughly investigated by exploiting the function of pyrene moieties as a molecular probe through measuring the fluorescence emission spectra at different times during the structure evolution. The photoluminescent (PL) intensity, excimer emission, and vibrational fine structure of the fluorescence spectra were observed to give information about phase separation and solidification occurred in the dispersed droplets. The observations were rationalized by analysis with ternary phase diagrams calculated on the basis of the Flory-Huggins theory. Upon irradiation with a linearly polarized laser beam at 488 nm, the azo polymer parts in the P(MMA-co-PyMA)/PCNAZO JPs were observed to be elongated along the electric vibration direction of the polarized light and transformed into particles with unique morphologies. The dispersions of JPs with different compositions of the two types of the polymers showed highly tunable color changes originating from both fluorescence of the pyrenyl fluorophores and light absorption of the azo chromophores.

2.
Langmuir ; 35(47): 15295-15305, 2019 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-31661623

RESUMO

In this work, photoinduced asymmetric morphology transformation of a type of azo molecular glass microspheres was thoroughly investigated to understand the effects of controlling factors on the process, related mechanism and unique functions. The monodispersed microspheres with their sizes over ten microns were fabricated from an isosorbide-based azo compound (IAC-4) by microfluidics. Under irradiation with linearly polarized light, the ten-micron-scale microspheres were transformed into three-dimensional (3D) asymmetric particles through directional mass transfer. Microscopic observations and optics simulation were employed to investigate the morphology transformations. The results show that the penetration depth of light at different wavelengths plays an extremely important role to affect the asymmetric deformation behavior of the IAC-4 microspheres, which determines deformation region, deformation degree and final shapes of the particles. The light intensity (50-200 mW/cm2) is a less important factor, while the deformation rate of the light-penetrated part linearly increases with the intensity. When the light intensity varies in this range, the deformation degree and the final asymmetric morphology are determined by exposure energy (light intensity × irradiation time). The IAC-4 microspheres with different sizes show distinct morphology transformation behavior and the deformed particles possess different shapes, caused by the variation of volume fraction of the light-penetrated part in the microspheres. The increase in the ratio of the light-penetrated part to the total volume of the microspheres results in larger scale deformations. Based on the above understanding, asymmetric particles with various morphologies can be fabricated through a precisely controllable way. The asymmetric particles loaded on various surfaces show ability to render remarkable wetting anisotropy of water droplets on the substrates.

3.
Adv Mater ; 31(16): e1804434, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30848003

RESUMO

Properly controlling the rheological properties of nanoparticle inks is crucial to their printability. Here, it is reported that colloidal gels containing a dynamic network of graphene oxide (GO) sheets can display unusual rheological properties after high-rate shearing. When mixed with polyaniline nanofiber dispersions, the GO network not only facilitates the gelation process but also serves as an effective energy-transmission network to allow fast structural recovery after the gel is deformed by high-rate shearing. This extraordinary fast recovery phenomenon has made it possible to use the conventional air-brush spray technique to print the gel with high-throughput and high fidelity on nonplanar flexible surfaces. The as-printed micro-supercapacitors exhibit an areal capacitance 4-6 times higher than traditionally spray-printed ones. This work highlights the hidden potential of 2D materials as functional yet highly efficient rheological enhancers to facilitate industrial processing of nanomaterial-based devices.

4.
Chem Asian J ; 13(19): 2781-2785, 2018 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-29969186

RESUMO

Three-arm star azopyridinium salts self-organize into various morphologies in water/organic mixed solvents. Interesting AIE and self-assembling features are observed due to the strong interaction of the azopyridinium moieties with the highly polar H2 O molecules causing the salts to aggregate, which restricts the molecular motion and induces the fluorescence.

5.
Soft Matter ; 14(28): 5847-5855, 2018 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-29957819

RESUMO

Azo molecular glass (IAC-4) microspheres with a monodispersed diameter over ten microns were fabricated by microfluidics and unique shape manipulation was achieved based on their fascinating photoinduced deformation behaviour. After irradiation with a polarized laser beam (λ = 488 nm), the IAC-4 microspheres were transformed into uniform mushroom-like particles, and their three-dimensional (3D) asymmetric shapes were precisely manipulated by adjusting the irradiation time and the polarization state of light. By observing the particle morphology in three orthogonal views (top view, front view and side view) by scanning electron microscopy (SEM), the photoinduced deformation behaviour of the ten-micron-sized particles was comprehensively revealed in the 3D space for the first time. It was observed that the photoinduced deformation asymmetrically occurred on the upper part of the microspheres due to the strong optical absorption of the azo chromophores. Besides, the deformation manner of the upper part was decided by the direction of the electric vibration of the refracted light. This work not only depicts a clear picture of the photoinduced deformation behaviour of the ten-micron-sized azo particles upon polarized light irradiation, but also provides a new method to controllably manipulate the particle shape from spheres to complex 3D architectures.

6.
Nanoscale ; 10(8): 4113-4122, 2018 Feb 22.
Artigo em Inglês | MEDLINE | ID: mdl-29435534

RESUMO

Herein we report a new approach to fabricating nanoscrolls through the self-assembly of graphene oxide (GO) sheets in a dispersion. The assembly process for GO nanosheets was induced by the dropwise addition of an appropriate organic solvent such as N,N-dimethylformamide (DMF) into the aqueous dispersion. The results show that nanoscrolls were gradually formed from the GO sheets by rolling-up in a piece-by-piece manner with the increase of the DMF content. The transmission electron microscopic analysis indicates that for a typical case, the nanoscrolls have an average diameter of 242 ± 102 nm at the central part and the interlayer spacing between adjacent GO layers is 0.58 nm. The scrolls were estimated to have 207 turns and include on average 42 pieces of GO sheets per scroll. By this method, GO sheets with different sizes and oxidation degrees were proved to be able to form GO nanoscrolls in a similar way. Moreover, it is interesting that the diffraction efficiency of surface-relief-gratings photoinduced on the film of azo molecular glass was significantly enhanced by doping the GO nanoscrolls with a very low content (0.5 wt%); this suggests a possible new application for the GO scrolls in optical devices. This facile approach, which is also feasible by using other organic solvents such as ethanol, can be used to fabricate GO nanoscrolls for large scale applications in supercapacitors, sensors and other devices.

7.
Langmuir ; 33(40): 10645-10654, 2017 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-28926714

RESUMO

This study investigated Janus and strawberry-like particles composed of azo molecular glass and polydimethylsiloxane (PDMS) oligomer, focusing on controllable fabrication and formation mechanism of these unique structures and morphologies. Two materials, the azo molecular glass (IA-Chol) and PDMS oligomer (H2pdca-PDMS), were prepared for this purpose. The Janus and strawberry-like particles were obtained from the droplets of a dichloromethane (DCM) solution containing both IA-Chol and H2pdca-PDMS, dispersed in water and stabilized by poly(vinyl alcohol). Results show that the structured particles are formed through segregation between the two components induced by gradual evaporation of DCM from the droplets, which is controlled by adding ethylene glycol (EG) into the above dispersion. Without the addition of EG, Janus particles are formed through the full segregation of the two components in the droplets. On the other hand, with the existence of EG in the dispersion, strawberry-like particles instead of Janus particles are formed in the phase separation process. The diffusion of EG molecules from the dispersion medium into the droplets causes the PDMS phase deswelling in the interfacial area due to the poor solvent effect. Caused by the surface coagulation, the coalescence of the isolated IA-Chol domains is jammed in the shell region, which results in the formation of the strawberry-like particles. For the particles separated from the dispersion and dried, the PDMS oligomer phase of the Janus particles can adhere and spread on the substrate to form unique "particle-on-pad" morphology due to its low surface energy and swelling ability, while the strawberry-like particles exist as "standstill" objects on the substrates. Upon irradiation with a linearly polarized laser beam at 488 nm, the azo molecular glass parts in the particles are significantly deformed along the light polarization direction, which show unique and distinct morphologies for these two types of the particles.

8.
Chem Asian J ; 11(23): 3443-3448, 2016 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-27706933

RESUMO

We report the successful fabrication of photoresponsive Janus particles (JPs) composed of an epoxy-based azo polymer and poly(methyl methacrylate) (PMMA). Two representative azo polymers, of which one polymer (BP-AZ-CN) has cyano groups as electron-withdrawing substituents on the azobenzene moieties and the other polymer (BP-AZ-CA) has carboxyl groups as the electron-withdrawing substituents, were adopted for the investigation. The nanoscaled JPs, with a narrow size distribution and different azo polymer/PMMA ratios, were fabricated through self-assembly in solution and as dispersions. Upon irradiation with linearly polarized light (λ=488 nm), two types of photoresponsive behavior were observed for JPs in the solid state. For JPs composed of BP-AZ-CN and PMMA, the light irradiation caused the azo-polymer component to be stretched along the light polarization direction. Conversely, for JPs composed of BP-AZ-CA and PMMA, the azo-polymer component became separated from PMMA component under the same irradiation conditions. These observations are valuable for a deeper understanding of the nature of self-assembly and photoinduced mass-transport at the nanometer scale.

9.
Chem Asian J ; 11(15): 2130-4, 2016 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-27309125

RESUMO

It is of great fundamental and practical significance to endow Janus particles with various field-responsive properties. In this study, a new strategy with a wide range of application possibilities is developed to fabricate JPs composed of a methacrylate-based azo polymer, polystyrene, and Fe3 O4 nanoparticles. The JPs are obtained through microphase separation in a confined volume of the dispersed droplets. The azo polymer and PS are incorporated in JPs in a core-compartmentalized manner, and Fe3 O4 are proved to exist in the azo polymer phase. The JPs show responsive movement in the magnetic field and can be easily oriented with the help of the field. By variation of the intersection angle between the particle symmetrical axis and the polarization direction of the linearly polarized laser beam, different deformation modes are feasibly achieved for the JPs. By exploiting the dual-responsive properties, JPs with designed shapes can be fabricated by exposing the JPs to linearly polarized light.

10.
ACS Appl Mater Interfaces ; 7(37): 20865-74, 2015 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-26323087

RESUMO

Flexible, transparent, and electrically conducting electrode materials are highly desired for flexible electronic applications. With a highly transparent polyimide (PI) as a substrate, a comprehensive and comparative study was performed to investigate four different fabrication schemes in producing transparent and electrically conducting SWCNT/PI electrodes. A very promising method that involves an in situ imidization process and nitric acid doping treatment was identified, which led to the fabrication of highly durable and thermally stable SWCNT/PI electrodes. The best performed electrode has a transmission of 77.6% at 550 nm and a sheet resistance (Rs) of 1169 ± 172 Ω/□, which appeared no changes after repeating tests of bending, folding-unfolding, adhesive-tape-peeling-off, and wet tissue-paper scratching/wiping. The excellent thermal stability of such fabricated SWCNT/PI electrode is manifested by the very high glass transition temperature of 290.1 °C and low coefficient of thermal expansion (CTE) of 28.5 ppm °C(-1) in the temperature range from 75 to 200 °C. The new method expects to be able to pave the way in facile production of high-performance flexible, transparent, and conducting electrodes.


Assuntos
Imidas/química , Nanotubos de Carbono/química , Poliaminas/química , Temperatura , Adesividade , Eletricidade , Eletrodos , Espectroscopia Fotoeletrônica , Espectrofotometria Ultravioleta
11.
ACS Appl Mater Interfaces ; 7(30): 16889-95, 2015 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-26168368

RESUMO

A novel 4-arm shaped amphiphilic azobenzene compound was synthesized. The tetraphenylethylene (TPE) core precursor was prepared and further modified by azo coupling reaction at the four peripheral groups. Colloidal spheres could be directly prepared by self-assembly of the prepared amphiphilic azobenzene compound in selective solvents (THF/H2O), which were characterized by using transmission electron microscopy. The colloid diameters could be controlled by adjusting the initial compound concentration and water-adding rate in the preparation processes. By irradiation with visible linearly polarized LED light (450 nm), fast photoinduced deformation of the colloidal spheres along the polarization direction was observed. A very large deformation degree (l/d > 4) could be easily obtained.

12.
Adv Mater ; 27(30): 4469-4475, 2015 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-26135240

RESUMO

Mechanically tough large-area hierarchical porous graphene films are fabricated by blade-casting of graphene oxide hydrogel and postcasting reduction. The as-prepared graphene films, which consist of well-exfoliated graphene nanosheets, possess interpenetrating 3D hierarchical porous structures, high strength and modulus, large specific area, and high electrical conductivity. Flexible film supercapacitors fabricated with the graphene electrodes show superior areal capacitance, good rate performance, and excellent mechanical stability.

13.
Macromol Rapid Commun ; 35(18): 1571-7, 2014 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-25132381

RESUMO

Nematic liquid crystalline elastomer (LCE) microactuators are developed, showing simultaneous thermomechanical deformation and photoluminescence (PL) emission variation functions. The microactuators are prepared by a method combining soft-lithography and photo-polymerization/crosslinking. 1,4-Bis(α-cyano-4-methoxystyryl)benzene as the PL dye is synthesized, characterized, and introduced into LCEs as a dopant in the preparation process. During the heating process, PL emission of the LCE micropillars under blue light excitation becomes significantly weak when the micropillars contract. When cooling down, the emission completely recovers as the micropillars stretches back to their original shape. The PL intensity variation at the transition is proved to be related to the thermomechanical deformation.


Assuntos
Elastômeros/química , Corantes Fluorescentes/química , Cristais Líquidos/química , Termodinâmica , Luz , Cristais Líquidos/ultraestrutura , Microscopia Eletrônica de Varredura , Microscopia de Fluorescência , Polimerização/efeitos da radiação , Espectrometria de Fluorescência , Espectroscopia de Infravermelho com Transformada de Fourier , Temperatura
14.
J Chem Phys ; 140(18): 184902, 2014 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-24832301

RESUMO

In this study, we simulated distortion and flow of nematics by dissipative particle dynamics (DPD). The nematics were modeled by a binary mixture that contained rigid rods composed of DPD particles as mesogenic units and normal DPD particles as solvent. Elastic distortions were investigated by monitoring director orientation in space under influences of boundary anchoring and external fields. Static distortion demonstrated by the simulation is consistent with the prediction of Frank elastic theory. Spatial distortion profile of the director was examined to obtain static elastic constants. Rotational motions of the director under influence of the external field were simulated to understand the dynamic process. The rules revealed by the simulation are in a good agreement with those obtained from dynamical experiments and classical theories for nematics. Three Miesowicz viscosities were obtained by using external fields to hold the orientation of the rods in shear flows. The simulation showed that the Miesowicz viscosities have the order of ηc > ηa > ηb and the rotational viscosity γ1 is about two orders larger than the Miesowicz viscosity ηb. The DPD simulation correctly reproduced the non-monotonic concentration dependence of viscosity, which is a unique property of lyotropic nematic fluids. By comparing simulation results with classical theories for nematics and experiments, the DPD nematic fluids are proved to be a valid model to investigate the distortion and flow of lyotropic nematics.

15.
Langmuir ; 30(2): 522-32, 2014 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-24378006

RESUMO

Photo-cross-linkable multilayer films composed of sulfonated reduced graphene oxide (SRGO) and polystyrene-based diazonium salt (PSDAS) were fabricated by electrostatic layer-by-layer (LbL) self-assembly. Polystyrene with narrow molecular weight distribution was synthesized by atom transfer radical polymerization (ATRP), and cationic PSDAS was prepared through nitration, reduction, and diazotization reactions. Negatively charged SRGO nanosheets were prepared through prereduced by NaBH4, modified by diazonium salt of sulfanilic acid, and then further reduced by hydrazine. The multilayer films were obtained by alternately dipping substrates in the PSDAS solution and SRGO dispersion in acidic conditions. The cross-linking between the components occurred during the multilayer formation process and was further achieved by the UV light irradiation after the film preparation. The assembling process and surface morphology of LbL multilayer films were monitored by UV-vis spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM). The cross-linking between SRGO and PSDAS was verified by attenuated total reflectance FTIR (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle measurement. The graphene nanosheets were found to be homogeneously distributed in the cross-linked network of the films. The large accessible surface area of graphene nanosheets and the cross-linking structure afforded the LbL films with high specific capacitance and excellent cyclic stability when used as supercapacitor electrodes. At a sweeping rate of 10 mV/s, the film with nine bilayers exhibited a specific capacitance of 150.4 F/g with ideal rectangular cyclic voltammogram. Large capacitance retention of 97% was observed after 10 000 charge-discharge cycles under the scanning rate of 1000 mV/s. This new approach for preparing graphene-containing multilayer films can be used to develop supercapacitor electrodes and other functional devices.

16.
J Chem Phys ; 139(10): 104902, 2013 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-24050360

RESUMO

In this study, dissipative particle dynamics (DPD) method was employed to investigate the translational diffusion of rodlike polymer in its nematic phase. The polymer chain was modeled by a rigid rod composed of consecutive DPD particles and solvent was represented by independent DPD particles. To fully understand the translational motion of the rods in the anisotropic phase, four diffusion coefficients, D∥(u), D⊥(u), D∥(n), D⊥(n) were obtained from the DPD simulation. By definition, D∥(n) and D⊥(n) denote the diffusion coefficients parallel and perpendicular to the nematic director, while D∥(u) and D⊥(u) denote the diffusion coefficients parallel and perpendicular to the long axis of a rigid rod u. In the simulation, the velocity auto-correlation functions were used to calculate the corresponding diffusion coefficients from the simulated velocity of the rods. Simulation results show that the variation of orientational order caused by concentration and temperature changes has substantial influences on D∥(u) and D⊥(u). In the nematic phase, the changes of concentration and temperature will result in a change of local environment of rods, which directly influence D∥(u) and D⊥(u). Both D∥(n) and D⊥(n) can be represented as averages of D∥(u) and D⊥(u), and the weighted factors are functions of the orientational order parameter S2. The effect of concentration and temperature on D∥(n) and D⊥(n) demonstrated by the DPD simulation can be rationally interpreted by considering their influences on D∥(u), D⊥(u) and the order parameter S2.

17.
J Chem Phys ; 139(8): 084109, 2013 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-24006976

RESUMO

We assess the accuracy and efficiency of two particle-based mesoscopic simulation methods, namely, Dissipative Particle Dynamics (DPD) and Stochastic Rotation Dynamics (SRD) for predicting a complex flow in a microfluidic geometry. Since both DPD and SRD use soft or weakly interacting particles to carry momentum, both methods contain unavoidable inertial effects and unphysically high fluid compressibility. To assess these effects, we compare the predictions of DPD and SRD for both an exact Stokes-flow solution and nearly exact solutions at finite Reynolds numbers from the finite element method for flow in a straight channel with periodic slip boundary conditions. This flow represents a periodic electro-osmotic flow, which is a complex flow with an analytical solution for zero Reynolds number. We find that SRD is roughly ten-fold faster than DPD in predicting the flow field, with better accuracy at low Reynolds numbers. However, SRD has more severe problems with compressibility effects than does DPD, which limits the Reynolds numbers attainable in SRD to around 25-50, while DPD can achieve Re higher than this before compressibility effects become too large. However, since the SRD method runs much faster than DPD does, we can afford to enlarge the number of grid cells in SRD to reduce the fluid compressibility at high Reynolds number. Our simulations provide a method to estimate the range of conditions for which SRD or DPD is preferable for mesoscopic simulations.

18.
ACS Appl Mater Interfaces ; 5(15): 7485-91, 2013 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-23848054

RESUMO

It is now well established that topological microstructures play a key role in the physical properties of surfaces. Stimulus-induced variations of topological microstructure should therefore lead to a change in the physical properties of microstructured responsive surfaces. In this paper, we demonstrate that roughness changes alter the wetting properties of responsive organic surfaces. Oriented nematic liquid crystalline elastomers (LCEs) are used to construct the microstructured surfaces via a replica molding technique. The topological microstructure of the surfaces covered with micropillars changes with temperature, due to the reversible contraction of the LCE pillars along the long axis at the nematic-to-isotropic phase transition. This is directly observed for the first time under environmental scanning electron microscopy (E-SEM). A high boiling point liquid, glycerol, is used to continuously monitor the contact angle change with temperature. The glycerol contact angle of the microstructured surfaces covered with small pillars decreases from 118° at room temperature to 80° at 140 °C, corresponding to a transition from Cassie state to Wenzel state.


Assuntos
Cristais Líquidos/química , Biomimética , Glicerol/química , Interações Hidrofóbicas e Hidrofílicas , Teste de Materiais , Microscopia Eletrônica de Varredura/métodos , Propriedades de Superfície , Temperatura , Água/química , Molhabilidade
19.
Chem Commun (Camb) ; 49(49): 5556-8, 2013 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-23673357

RESUMO

In this communication, a novel photochromic molecular switch DTE-2(Azo-CN) containing both dithienylethene and push-pull azo chromophores was synthesized. The push-pull azo chromophores can significantly accelerate the ring opening of the C-C bond of DTE closed isomer when irradiated with light far away from the maximum absorption band of the DTE closed isomer.


Assuntos
Compostos Azo/química , Etilenos/síntese química , Tiofenos/síntese química , Ciclização , Etilenos/química , Estrutura Molecular , Processos Fotoquímicos , Tiofenos/química
20.
Chem Commun (Camb) ; 49(53): 5957-9, 2013 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-23715375

RESUMO

The aptamer-functionalized hydrogel diffraction gratings were successfully fabricated by incorporating an aptamer and its complementary sequence as crosslinking junctions in the network structure. The gratings showed a sensitive response to human thrombin as read out from the diffracted light.


Assuntos
Aptâmeros de Nucleotídeos/química , Técnicas Biossensoriais , Hidrogéis/química , Trombina/análise , Humanos , Dispositivos Ópticos , Trombina/química
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA